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CSD modem connection issues

artyb Mar 19, 2020 04:44 AM


Firstly, I know that the days of landlines and CSD are both numbered, but we have existing systems using this comms route.

We have a few sites that we’re struggling to connect to, via a landline analogue modem to CSD cellular modems. One of our clients is able to connect to the sites. I’ve tried different modems, with some improvement.

Do you have any insight/advice as to why different modems may perform better than others, and what we could do to improve this? It shouldn’t be down to remote signal strength as our client can connect. Might it be down to serial data timing and autobauding?

On one site in a different country we are still having issues. We can mostly conenct to the modem, but apparently not to the logger. The Low Level Log shows:

..CONNECT 9600..











This looks to me as though LoggerNet is sending a connect/hello but not getting a reply from the logger. Is that right?

Is there any documentation on these autobauding and commands sent (eg the q and ' seen in the logs)?

Would you recommend not using autobauding?

We usually set the default logger baud rate to match the modem, but allow auto bauding so that eg a laptop can connect at a faster rate on a site visit. I'm wondering if the autobauding from the ring isn't working, and the logger is moving to a different baud rate?

It's odd that our client can connect from the same country though. Maybe different telecoms operators have different equipment routing the signal which makes the difference?

Thank you,


JDavis Mar 20, 2020 03:29 PM

Using fixed baud rates is definitely recommended. If the connection works from the other office, the baud rates on the equipment in the field is not the issue.

The likely culprits are:

Quality of landline at the office

PC modem used

Modem dial string used in Loggernet

artyb Mar 23, 2020 06:37 AM


Thanks for the reply. Can you tell me what the dots and q in the logs mean?

Any recommendations for PC modem?

Can you elaborate about the modem dial string in loggernet? Are there some options I could try?

I was wondering if the remote autobauding between logger attached modem could be thrown off if the signal from our line is distorted?

Best Wishes,


JDavis Mar 23, 2020 10:39 AM

The dots represent unprintable characters.

When the dial string entry box in Setup has focus(cursor inside box) push F1 to open help. That will give you help on the dial string. You will need to check your modem manual to see which AT commands it supports.

The best PC modems we have seen are external modems built by US Robotics.It looks like the current model is USR5686G

artyb Mar 24, 2020 04:19 AM


What do the q and ' indicate?

Could you give me an example of dial strings that might improve unreliable comms? I think you're refering to the logger settings, rather than LoggerNet where the only settings I can see are by editing the modem database. I'd have to establish a connection or visit site to change the logger settings though...

We have mainly used USR (admittedly older ones ~15-20 years old now). They tell me that their circuitry hasn't changed, but maybe some components in our modems had degraded. I've recently had more success with a different (now discontinued) modem, except for this one site.



artyb Apr 23, 2020 04:55 AM

Could you tell me what the q and ' indicate?

Could you give me an example of dial strings that might improve unreliable comms? I think you're refering to the logger settings, rather than LoggerNet where the only settings I can see are by editing the modem database, and there isn't a dial string that I can find? I'm not sure where you mean?

I'd have to establish a connection or visit site to change the logger settings though...

It's odd that all sites other than this one work, which would suggest that the issue isn't with the modem or line? And our client can connect without issues.

artyb Sep 11, 2020 05:31 AM

Could I bump this? Responses to the previous post questions would be great please to help me understand what the issue is.

I've started seeing this on another site, but have the same serial log when calling from a landline or cellular modem, suggesting that the issue is at the remote site.

jtrauntvein Sep 11, 2020 08:08 AM

PakBus, which is the protocol used to communicate with the datalogger is a binary protocol which can make use of any of the byte values between 0 and 255 (0xFF).  When the low level log file is formatted, the content being sent or received is formatted in both a hex representation and an ASCII representation.  Because PakBus is binary, the ASCII representation is mostly meaningless and the hex representation is what must be relied upon to interpret what is being sent or received.  There is a program included with LoggerNet called LogView that can be invaluable in interpreting these logs.  You can find the program in the LoggerNet install directory (generally "C:\Program Files (x86)\CampbellSci\LoggerNet\logview.exe).  You can open the low level log within this program using the File/Open Log menu item and, once the log is shown, you can look at this with the PakBus Filter by invoking the View/Add PakBus Filter menu item.  The resulting view will allow you to single step through each of the PakBus packets that appear in the log and will show a decoding window for each of these packets. 

artyb Sep 11, 2020 08:55 AM

Aha, that seems like a good step towards being able to diagnose issues. I didn't know that program existed. I've browsed to C:\Campbellsci\LoggerNet\logs and opened what I think is the latest log for the route in question. It starts just after noon yesterday. Is that what would be expected? I'm struggling to use the Find to jump to the right part of the log file though. Does that filter on ASCII or hex (I've tried both).

Also on the PakBus view how do I select a packet? I can't get that filter/find to work either?

I can't find much documentation for Log File Viewer?



artyb Sep 16, 2020 05:39 AM

OK, I've been able to search for the phone number to find the right part of the files, and open the pakbus filter tab. How do I use that tab though? The display shows the same hex and ASCII as in the normal low-level log view, and says that "There is no packet selected" How do I select a packet? How do I use the pakbus filter? I can't find much documentation on how to use this program?


artyb Sep 16, 2020 05:59 AM


I think I've made some progress after finding an old guide to pakbus. Pressing the 'Next' button shows more info on the pakbus packets. Not sure how to go back through the logfile to before the place it starts from, but the pakbus filter starts close to where the ASCII filter was on the previous tab at least.

I'm seeing

ring (9) link state (0) {..........q.....}

Expect More: neutral (2) off line (8) {........`.}

ring (9) link state (0) {.....q..}

ring (9) link state (0) {.....q..}

ring (9) link state (0) {.....q..}

ring (9) link state (0) {.....q..}

So it looks like the modem is sending the RING signal to the logger but the connection isn't being made, which is what I suspected. Is this baud rate negotiations failing?

However I don't know why that is the case from one calling modem and not from another (which it works from fine)?

Any other insights?



artyb Sep 24, 2020 03:27 AM

I'd welcome any more disgnosis suggestions, or info as to what may be causing this please?

artyb Oct 21, 2020 09:42 AM

Could I bump this again please? Can anyone add suggestions as to what the cause could be, how to investigate and resolve it?

Thank you,

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